Method of adjusting a signal power in a variable data rate mode in a mobile communication system

ABSTRACT

The present invention relates to a mobile communication system, and more particularly, to a method of adjusting a signal power in a variable data rate mode. Accordingly, the present invention includes steps of allocating a reference pilot signal level to each of a plurality of data rates supported by the system and adjusting the reference pilot signal level for a changed data rate based on an external control information and adjusting a power control threshold for secondly adjusting the reference pilot signal level corresponding to the reference pilot signal level.

This application claims the benefit of the Korean Application No.P2001-55091 filed on September, 07, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication system, and moreparticularly, to a method of adjusting a signal power in a variable datarate mode in a mobile communication system.

2. Discussion of the Related Art

Generally, in a 3^(rd) generation mobile communication system of a CDMAtype, a mobile station has a multi-channel structure that simultaneouslytransmits several traffic channels in order to provide diversemultimedia services such as voice, image, and data in addition totransmitting only one traffic channel as in the IS-95A.

Also, in a reverse link, a base station performs a coherent demodulationin order to improve the performance. The mobile station transmits apilot channel along with a plurality of traffic channels so that thebase station performs the coherent demodulation of the traffic channels.

A traffic-to-pilot power ratio is determined in accordance with a codingrate, a desired signal-to-interference ratio (SIR), a transmission rate,etc.

FIG. 1 is a block diagram explaining a conventional process ofgenerating a multi-channel transmission signal.

As shown in FIG. 1, a mobile station passes a pilot channel and trafficchannels (i.e., a dedicated control channel, a supplemental channel, anda fundamental channel) through a spreading unit 110 and a basebandfilter 106 to transmit the channels to a base station.

At this time, gains of the respective traffic channels are adjustedthrough a relative gain section 102 before being spread so that thetraffic channels are transmitted with relative transmission power ratiosG_(F), G_(C), and G_(S) of the traffic channels to the pilot channel.

Here, G_(F) represents a value of the relative transmission power ratioof the fundamental channel for transmitting information such as voiceand so on, G_(C) represents a value of the relative transmission powerration of the dedicated control channel used to transmit dedicatedcontrol information, and G_(S) represents a value of the relativetransmission power ratio of the supplemental channel used to transmitdata.

The transmission power of the pilot channel is adjusted by a closed-looppower control through a reverse link.

The transmission power control of the traffic channels is performed in amanner that the transmission power ratio of the traffic channel to thepilot channel is maintained constantly.

The closed-loop power control is classified into two following types.

First, an inner-loop power control type measures thesignal-to-interference ratio (SIR) of a received signal from a signalpower of the pilot channel to compare the SIR with a power controlthreshold value, and transmits power control bits through a forwardlink.

Second, an outer-loop power control type periodically adjusts the powercontrol threshold value in order to maintain a frame error rate (FER)desired by a radio channel that changes according to time.

At this time, the threshold value of power control to be used in areceiving end for each data rate is differently defined. In other words,the power level of a reference pilot signal to be used in a sending endfor each data rate is differently defined.

Also, the power ratio of the traffic signal to the pilot signal isdifferently defined for the respective data rate.

Meanwhile, there have been proposed a 1× cdma2000 system designed tosupport a voice service of a circuit switched mode and anintermediate-speed and high-speed data service, a high data rate (HDR)or 1×-evolution data only (1×-EV DO) system proposed only for ahigh-speed packet data communication, and a 1×-evolution data and voice(1×-EV DV) system that is an integrated version of the two systems asdescribed above. The data rate control in the above systems is performedas follows. Hereinafter, these systems will be generically named a 1×system.

There is a variable data rate mode among operation modes of theconventional 1× system.

Especially, in the variable data rate mode in the reverse link, a set ofdata rates fixed to one another should be defined between the mobilestation and the base station in a negotiation stage.

Generally, in defining the data rate set, about 3 data rates aredetermined as a hypothesis set for the variable data rate, and themobile station automatically changes the data rates within the set.

Specifically, if the mobile station judges the remaining power is notsufficient to maintain the present data rate as it is checking theremaining power that can be used by itself, it changes its own data rateto a lower data rate existing in the hypothesis set.

Then, the base station recognizes the changed data rate through a blindrate detection.

At this time, in order to control the signal power corresponding to thechanged data rate, the 1× system uses the following methods.

As described above, the power ratio of the traffic signal to the pilotsignal should be changed for the respective data rates. That is, in caseof a high data rate, the level of the received pilot signal should alsobe heightened. As described above, if the power level of the receivedpilot signal is separately controlled for the respective data rate, thevariable data rate operation becomes impossible. That is, since the datarate of the reverse link currently transmitted cannot be known until thebase station completely receive one frame, it is impossible to determinethe power control threshold value to be used in the inner loop.

In order to solve the above-described problem, there has been proposed amethod of using the reference pilot power level for the maximum datarate allocated in the hypothesis set with respect to other data rates inthe hypothesis set. That is, in case of using the power level of thereference pilot signal to the maximum data rate in other data rates inthe hypothesis set, i.e., in case that the mobile station transmits thecorresponding signal with a data rate different from the maximum datarate, the power ratio value of the supplemental channel signal to thepilot signal becomes different from the original power ratio value.

An example of this process will now be explained.

It is assumed that the hypothesis set to be used is put as {9.6 kbps,19.2 kbps, 38.4 kbps} through the negotiation stage between the mobilestation and the base station. In this case, the optimum power ratios ofthe pilot signal to the traffic signal are determined as follows for therespective data rates.

(Pilot:Traffic)=(1:2.37), 9.6 kbps

(Pilot:Traffic)=(1.02:4.3), 19.2 kbps

(Pilot:Traffic)=(1.37:7.7), 38.4 kbps

At this time, the power ratios of the traffic signal to the pilot signalfor each data rate used in the variable data rate will be (1.37:2.37),(1.37:4.3), and (1.37:7.7) with respect to 9.6 kbps, 19.2 kbps, and 38.4kbps, respectively.

Next, the variable data rate used in the 1×-EV DO system is driven inthe following manner.

First, the mobile station has a set of 5 transmission data rates {9.6kbps, 19.2 kbps, 38.4 kbps, 76.8 kbps, 153.6 kbps}.

The mobile station starts the transmission with the minimum data rate of9.6 kbps. Then, for each frame transmission time point, the mobilestation performs a p-persistent test, and increases the data rate by onestage only in case of passing this test.

At this time, the probability value that the mobile station increasesthe data rate in the set of the above-described data rates gets smalleras the data rate becomes higher.

Then, the base station measures the power level of an interferencesignal, and if the power level of the interference signal becomes higherthan a certain threshold value during the measurement, it generates acommon reverse activity (RA) bit to transmit the common RA bit to themobile stations.

The mobile stations that received the RA bit perform the p-persistenttest, and only the mobile stations determined to lower the rate duringthe test lower the data rate by one stage.

The mobile station should accurately transfer the data rate selectedduring the above process to the base station through a reverse rateindicator (RRI) channel.

In the variable rate operation process as described above, the powerlevel of the reference pilot signal to the lowest data rate in the setof 5 data rates is also used in other data rates in the set, and thebase station sets the power control threshold value to the pilot signalto be used in the inner-loop power control on the basis of the referencepilot power level.

The above-described methods, however, have the following problems ifthey are used in the variable data rate operation process considered inthe 1×-EV DV system.

The set of variable data rates currently considered is {9.6 kbps, 19.2kbps, 38.4 kbps, 76.8 kbps, 153.6 kbps, 307.2 kbps, 614.4 kbps, 1024kbps} that has 8 data rates.

In this case, if the power level of the reference pilot signal to themaximum data rate of 1024 kbps is used for all the data rates that canbe supported in the system, the power of the pilot signal becomesexcessively large in comparison to the power of the data to be sent.

As a result, it brings the excessive increase of overhead.

Even if the power level of the reference pilot signal of 153.6 kbps thatis an intermediate data rate is used, the power of the pilot signalcannot provide the power sufficient for demodulation of 8PSK that isused in 1024 kbps. Also, the use of the power level of the referencepilot signal of 9.6 kbps that is the minimum data rate cannot providethe reference pilot signal level sufficient for the operation of 1024kbps or 614.4 kbps.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method ofcontrolling a power of a pilot signal in a variable data rate mode thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a method of adjusting asignal power suitable to determine a power control threshold value in avariable data rate mode.

Another object of the present invention is to provide a method ofadjusting a signal power that does not increase an overhead of a pilotsignal in a variable data rate mode.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of adjusting a signal power in a variable data rate mode in amobile communication system, comprises steps of allocating a referencepilot signal level to each of a plurality of data rates supported by thesystem, adjusting the reference pilot signal level for a changed datarate based on an external control information and adjusting a powercontrol threshold for secondly adjusting the reference pilot signallevel corresponding to the reference pilot signal level.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a block diagram explaining a conventional process ofgenerating a multi-channel transmission signal.

FIG. 2 is a view illustrating a data rate changing procedure in avariable data rate mode according to the present invention.

FIG. 3 is a timing chart for a data rate control between a base stationand a mobile station according to the present invention.

FIG. 4 is a flowchart illustrating a power control process of a mobilestation according to the present invention.

FIG. 5 is a view illustrating an example of a power control change in abase station and a pilot power level change in a mobile stationaccording to the process of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention proposes a method of changing a power level of areference pilot signal, a power ratio of a pilot signal to a trafficsignal according to the power level of the reference pilot signal, and apower control threshold value to the pilot signal of an inner powercontrol loop to be used in a base station in case that a variable datarate is performed through a dedicated type rate control with respect toa channel for transmitting packet data in a reverse link of a 1×-EV DVsystem.

First, data rates considered in the reverse link are 8, i.e., {9.6 kbps,19.2 kbps, 38.4 kbps, 76.8 kbps, 153.6 kbps, 307.2 kbps, 614.4 kbps,1024 kbps}.

For convenience' sake, the channel for transmitting the packet data inthe reverse link will be called a reverse packet data channel (R-PDCH).Also, it is assumed that a sending end in the reverse link is a mobilestation, and a receiving end is a base station.

If the mobile station has data to be sent, it starts transmission ofpackets with the minimum data rate of 9.6 kbps even without permissionof the base station. Here, the mobile station cannot start the packettransmission to the base station with any other data rates except forthe minimum data rate.

The base station estimates reverse quality information between themobile station and the base station, and generates a dedicated reverserate control (RRC) bit.

The base station transmits the dedicated RRC bit to the correspondingmobile station, and controls the mobile station to heighten, or lowerthe data rate of the R-PDCH or to maintain the original data rate.

The mobile station, after receiving the dedicated RRC bit, adjusts thedata rate of the R-PDCH corresponding to the control bit, and transmitsthe adjusted data rate to the base station through a reverse rateindicator (RRI) channel of the reverse link. This is for the basestation to accurately know the changed data rate of the mobile station.

In the variable data rate transmission mode, it is necessary for themobile station to change the reference pilot power level for thetransmission power control of other signals (i.e., traffic signals fortransmitting the voice, image, and dedicated control information). Asdescribed above, this is because the mobile station operating in thevariable data rate mode cannot use one fixed reference pilot power levellike the existing 1× system since the number of data rates in thehypothesis set is 8.

Also, the process of changing the reference pilot power level and thepower control threshold value for the base station's generation of thereverse power control information according to the pilot power levelshould be performed accurately at a consistent time point between thebase station and the mobile station. If the time point is not consistentbetween the base station and the mobile station, malfunction of thepower control may be produced.

Accordingly, it is necessary to change the reference pilot power levelduring the operation process of the variable data rate, and thereference pilot power level is adjusted through three different methodsas follows.

First is a method of changing the pilot power level using anupper-signaling message.

In this method, the 8 data rates are classified into three groups. Thethree resultant groups are expressed as follows.

Group A: {9.6 kbps, 19.2 kbps, 38.4 kbps, 76.8 kbps}

Group B: {38.4 kbps, 76.8 kbps, 153.6 kbps, 307.2 kbps}

Group C: {153.6 kbps, 307.2 kbps, 614.4 kbps, 1024 kbps}

The respective groups have reference pilot power levels to be used intheir own groups. These reference pilot power levels are values selectedso that the operations of all the data rates in the respective groupsbecome optimum.

Based on the reference pilot power level determined as above, the powerratios of the pilot signal to the traffic signal are determined for thedata rates in the respective groups.

Using the groups defined as above, the data rate control and the powercontrol in the variable data rate mode between the mobile station andthe base station are performed.

FIG. 2 is a view illustrating the data rate changing procedure in thevariable data rate mode according to the present invention.

In case that the mobile station has the packet data to be sent, italways starts transmission of the R-PDCH using the minimum data rate of9.6 kbps.

Thus, the mobile station starts the data transmission in the group A.Here, the reference pilot signal power that is used by the mobilestation becomes the reference pilot signal power of the group AP_(REF,A).

The mobile station receives the dedicated RRC bit from the base stationand checks the dedicated RRC bit (step S10).

The mobile station, according to a command indicated by the RRC bit(step S11 or S12), maintains or heightens the present data rate (stepS16 or S20).

In case of heightening the present data rate, the mobile station changesthe traffic signal power, but does not change the reference pilot powerlevel. However, in case of maintaining the present data rate, the mobilestation does not change the traffic signal power and the reference pilotpower level.

Thereafter, the mobile station judges whether the data rate of thesignal transmitted by the mobile station is the maximum data rate in thegroup to which the mobile station itself belongs (step S17). Forinstance, if the data rate is 76.8 kbps in the group A, the mobilestation transmits a request message for changing the group to the basestation in order to change its belonging group to the group B (stepS18).

The base station transmits an approval message to the mobile station inresponse to the change request message.

The mobile station that received the approval message changes the groupto which it belongs to the group B. Then, the mobile station uses thereference pilot signal power P_(REF,B) defined in the group B and thepower ratio of the pilot signal to the traffic signal for the respectivedata rate (steps S13 and S14).

During this process, the mobile station can first change the presentdata rate to the data rate outside the group to which the mobile stationitself belongs before it receives the approval message from the basestation in response to the group change request message sent by itself.

However, the mobile station that could not receive the approval messagemaintains the reference pilot power level of the present group (stepS15). Accordingly, the mobile station uses the value of the referencepilot power level defined in its belonging group, transmits the presentframe by determining the traffic power level corresponding to thechanged or maintained data rate, and then prepares the transmission ofthe next frame (step S20).

In the same manner, if the transmission data rate becomes 307.2 kbpswhile the mobile station in the group B continues the signaltransmission to the base station, the mobile station changes itsbelonging group to the group C through the same process as describedabove, and uses the reference pilot power level P_(REF,C) of the groupC.

The above-described process is also applied to the process of loweringthe data rate in the same manner.

The mobile station, according to the command indicated by the RRC bit(step S12), lowers the present data rate (step S21). In case ofdecreasing the present data rate, the mobile station changes the trafficsignal power, but does not change the reference pilot power level.

Thereafter, the mobile station judges whether the data rate of thesignal transmitted by the mobile station is the minimum data rate in thegroup to which the mobile station itself belongs (step S22). Forinstance, if the data rate is 153.6 kbps in the group C, the mobilestation transmits a request message for changing the group to the basestation in order to change its belonging group to the group B (stepS23).

The base station transmits an approval message to the mobile station inresponse to the change request message.

The mobile station that received the approval message changes the groupto which it belongs to the group B. Then, the mobile station uses thereference pilot signal power P_(REF,B) defined in the group B and thepower ratio of the pilot signal to the traffic signal for the respectivedata rate (steps S13 and S14).

During this process, the mobile station can first change the presentdata rate to the data rate outside the group to which the mobile stationitself belongs before it receives the approval message from the basestation in response to the group change request message sent by itself.

However, the mobile station that could not receive the approval messagemaintains the reference pilot power level of the present group (stepS15). Accordingly, the mobile station uses the value of the referencepilot power level defined in its belonging group, transmits the presentframe by determining the traffic power level corresponding to thechanged or maintained data rate, and then prepares the transmission ofthe next frame (step S20).

In the same manner, if the transmission data rate becomes 38.4 kbpswhile the mobile station in the group B continues the signaltransmission to the base station, the mobile station changes itsbelonging group to the group A through the same process as describedabove, and uses the reference pilot power level P_(REF,A) of the groupA.

Specifically, the change of the group is effected according to thefollowing rule.

The base station, after sending to the corresponding mobile station theapproval message in response to the group change request of the mobilestation, changes the power control threshold value (i.e., a value forgenerating a reverse power control bit to be transmitted to the mobilestation) to be used in the base station after a predetermined delay time(corresponding to the predetermined number of frames) in accordance withthe reference pilot power level to be transmitted from the mobilestation.

(1) (Group A→Group B), (Group B→Group C): a rule of the group change incase of heightening the data rate

(2) (Group B→Group A), (Group C→Group B): a rule of the group change incase of lowering the data rate

The reason why the group B is used during the above process is to put abuffer zone for lowering the frequent generation of the messageaccording to the change of the data rate.

Second is a method whereby the mobile station changes a reference pilotpower level in a variable data rate mode using a direct command of aphysical layer, instead of using a message of an upper layer. Thismethod will now be explained with reference to FIG. 3.

In this method, the time point when the reference pilot power level ischanged between the base station and the mobile station is engaged asfollows.

First, in case that the base station generates a dedicated RRC bit forthe data rate control of the mobile station, the following is assumed.

After generating the RRC bit that once changes the data rate, the basestation does not change the data rate change command for the time of(n−1) frames. As a result, the data rate change rate is considered to beactually (50/n) Hz.

The mobile station, after receiving the RRC bit, determines its owntransmission data rate, and transmits the data rate to the base stationthrough the reverse rate indicator (RRI) channel.

The base station can judge what operation the mobile station isperforming with respect to the RRC bit transmitted by the base stationitself just after it receives the RRI channel.

After continuing the confirmation of the RRI for the time of n frames,the base station changes the threshold value to be used in the powercontrol using the reference pilot power level corresponding to the datarate that is considered to be sent by the mobile station.

The mobile station transmits the signal to the base station with thesame data rate continuously for the time of n frames, matches only thepower of the traffic signal to the transmission data rate, and maintainsthe previous value of the reference pilot signal.

Just after the time of n frames elapses, the mobile station changes thereference pilot signal level.

Through the above process, the mobile station and the base station canchange the value of the reference pilot signal level and the thresholdvalue to be used in the power control at an accurate time point.

At this time, the information of the RRI channel additionally includesan index bit for informing the order of the present RRI channel.

FIG. 3 is a timing chart for the data rate control between the basestation and the mobile station according to the present invention.

Here, it is assumed that the number N of frames is 4. The time delay forthe transmission of the frames between the base station and the mobilestation is not considered. MS Rx and BS Rx represent receiving parts ofthe mobile station and the base station, and MS Tx and BS Tx representsending parts of the mobile station and the base station.

Referring to FIG. 3, at a time point 1, the base station generates theRRC control bit, and transmits the generated RRC control bit to themobile station.

At the time point 1′, the mobile station receives the RRC bit,determines the data rate to be sent to the next frame, and startstransmission of the frame having the determined data rate to the basestation at a time point 2 (in FIG. 3, it is also called C).

At this time, the power of the traffic signal in the mobile stationshould be determined according to the adjusted data rate, and the powerlevel of the reference pilot signal is maintained to the previous value.Also, the data rate transmitted at the time point 2 should be alsomaintained at frame time points 3, 4, and 5. That is, the data ratetransmitted at the time point is maintained for 4 frames.

From the time point 2 to the time point 5, the mobile stationcontinuously informs the present data rate to the base station throughthe RRI channel, and in order to inform the order of the RRI channelbeing now transmitted, the RRI channel includes the time indexes of (0,1, 2, 3). In FIG. 3, the numerals in parentheses of BS Rx and MS Txindicate time index values. In order to include and transmit the timeindex, th RRI channel requires additional information of 2 bits.

After the time for 4 frames elapses, the reference pilot power levelvalue to be used in a transmission time point 7 (in FIG. 3, it is alsocalled D) is changed based on the data rate previously used.

The base station receives the RRI channels at time points 2′, 3′, 4′,and 5′. Even when only one among the 4 RRI channels is properlyreceived, the base station changes the power control threshold value tobe applied at a time point 7′ (in FIG. 3, it is also called A) using thedata rate indicated by the received RRI channel.

The above process is continuously repeated (at time points 6, 7, 8, 9,and 10).

Through the above-described process, the time point of the change of thereference pilot power level to be used by the mobile station and thethreshold value to be used during the power control procedure of thebase station can be accurately checked.

Third is a method whereby the base station automatically changes a powercontrol threshold value and the mobile station automatically changes areference pilot power level.

In the third method, the mobile station changes the reference pilotpower level using a specified algorithm for itself without anyinstructions received, and in the same manner, the base station detectsthe effective data rate transmitted from the mobile station through theRRI channel, and uses the power control threshold value corresponding tothe effective data rate.

The third method is for solving the following special case.

If the base station uses a lower power control threshold value and themobile station changes in advance the reference pilot power level to ahigher level, the base station will compare the received pilot powerlevel with the power control threshold value, and transmit a power-downcommand to the corresponding mobile station in succession.

In this case, the time point when the base station detects that thereference pilot power level of the mobile station is heightened will bethe time point after the base station receives the RRI channel anddecodes the data rate for the present frame.

However, due to the difference between the power control threshold valueof the base station and the reference pilot power level of the mobilestation, the base station frequently transmits the power-down command tothe mobile station, and this causes the receiving power level of the RRIchannel transmitted from the mobile station to become lower than thereceiving power level where the base station can perform a properdecoding. As a result, the base station may not detect the data ratecurrently used by the mobile station, and thus the performance of thesystem may be greatly deteriorated.

Accordingly, the present invention heightens the reference pilot powerlevel to be used by the mobile station after the base station heightensin advance the power control threshold value by setting a time delay ofN frames at maximum in case that the mobile station heightens thereference pilot power level.

On the contrary, in case that the mobile station lowers in advance thereference pilot power level and the base station uses the high powercontrol threshold value, big trouble is not produced.

In this case, the base station continuously generates the power-upcommand by comparing the received pilot power level with the powercontrol threshold value, and after properly receiving the RRI channeltransmitted from the mobile station, it can apply the changed powercontrol threshold value. Based on such assumption, the followingflowchart of FIG. 4 can be obtained.

FIG. 4 is a flowchart illustrating the power control process of themobile station according to the present invention.

Among parameters used in FIG. 4, R_(eff)(i) is an effective data rateadjusted by the reverse dedicated data rate control at an i-th frametime. It is to be noted that this effective data rate is a combined datarate of a reverse new packet data channel (R-NPDCH) and a reverseretransmission packet data channel (R-RPDCH) in case of considering ahybrid automatic repeat request (ARQ) request.

The present invention uses a method of re-transmitting the packet inwhich NACK is transmitted from the receiving end and multiplexing thetransmission of a new packet. At this time, the multiplexing techniquethat is considered for multiplexing the re-transmitted packet and thenew packet is classified into two methods, i.e., a code divisionmultiplexing (CDM) and a time division multiplexing (TDM)

For this, the following channels are defined on the reverse link.

First, the channel for the reverse packet transmission is called areverse packet data channel (R-PDCH). The R-PDCH is composed of twokinds of sub-channels, i.e., a reverse new packet data channel (R-NPDCH)used for transmission of a new packet and a reverse retransmissionpacket data channel (R-RPDCH) for transmission of a re-transmittedpacket.

The two sub-channels as above are multiplexed using the CDM or TDMmethod.

First, in case of using the CDM method, the R-NPDCH and the R-RPDCH aretransmitted on independent physical channels using different Walshcodes.

In case of using the TDM method, the retransmission and the newtransmission are multiplexed in time on one physical channel using oneWalsh code.

N represents the number of delayed frames with respect to the changedpilot power level, and has a fixed value.

PL(i) represents a pilot level (PL) changed at the i-th frame time.

PL[R_(eff)(i)] represents a predefined pilot level with respect to theeffective data rate R_(eff)(i)

At this time, the data rate of the R-NPDCH itself may be the R_(eff)(i)or “0”.

At this time, the following process is required according to the presentinvention.

The mobile station should accurately indicate the current data rate tothe base station through the RRI channel. At this time, it is assumedthat the data rate indicated by the mobile station to the base stationis the R_(eff)(i). As described above, since the transmission data rateof the packet initially sent is 9.6 kbps, the R_(eff)(i) is 9.6 kbps,and at this time, the reference pilot power level PL(−1) is equal toPL(9.6 kbps) set from 9.6 kbps (step S30).

The mobile station preferentially checks the RRC bit from the basestation (step S31), and grasps what command the base station sent forthe transmission data rate control (step S31).

According to a command for increasing or maintaining the data rate, themobile station judges whether it can heighten or maintain the data ratein accordance with its status (step S32 or S33), and if it is judgedpossible, it calculates the effective data rate R_(eff)(i) at the i-thframe time. In the present invention, it is exemplified that thecalculated R_(eff)(i) becomes twice greater than or is equal to theeffective data rate at the previous frame time (step S34 or S35).

According to a command for decreasing the data rate, the mobile stationcalculates the effective data rate R_(eff)(i) at the i-th frame time. Inthe present invention, it is exemplified that the calculated R_(eff)(i)becomes smaller than the effective data rate at the previous frame timeby ½ (step S36). Then, the value of the reference pilot power levelPL[R_(eff)(i)] corresponding to the R_(eff)(i) calculated as above isreferred (step S37) Next, the mobile station checks whether theeffective data rates for the predetermined N-frame delay time are alwayslarger than or equal to the effective data rate at the (i−N)-th frametime (step S38).

If the effective data rates for the predetermined N-frame delay time arealways larger than or equal to the effective data rate at the (i−N)-thframe time, the mobile station sets the reference pilot power level atthe i-th frame time to the PL[R_(eff)(i−N)] value (step S40). If not,the mobile station compares the reference pilot power level PL(i−1) usedat the previous frame time with the reference pilot power levelPL[R_(eff)(i)] of the present effective data rate (step S39), and if thereference pilot power level PL(i−1) used at the previous frame time isgreater than the reference pilot power level PL[R_(eff)(i)], the mobilestation instantly changes the reference pilot power level to be used inthe present frame to the PL[R_(eff)(i)] (step S41).

If the reference pilot power level used at the previous frame time issmaller than or equal to the reference pilot power level PL[R_(eff)(i)],the reference pilot power level is not changed (step S42).

Thereafter, the traffic power level of the R-NPDCH is defined by thedata rate, and the traffic level of the R-RPDCH is defined by an energyreduction factor (step S43).

Here, by using the energy reduction factor, the traffic to pilot powerratio of R-RPDCH is reduced by a constant amount from the traffic topilot power ratio defined for the corresponding data rate on R-NPDCH sothat the receiving power level of the retransmitted data on R-RPDCH isreduced for a constant rate from the initially transmitted data onR-NPDCH.

Thereafter, the mobile station transmits the i-th frame according to theobtained reference pilot power level and the traffic power level, andprepares transmission of the next frame (step S44).

In case that the mobile station changes the reference pilot power levelas above, the base station preferentially searches for the effectivedata rate R_(eff)(i) of the present frame by decoding the RRI channel,and changes the power control threshold value to be used in the basestation to match the effective data rate.

FIG. 5 is a view illustrating an example of the power control change inthe base station and the pilot power level change in the mobile stationaccording to the process of FIG. 4.

FIG. 5 shows an example of the change of the pilot power level of themobile station according to the process of FIG. 4 if it is assumed thatN=2.

As shown in FIG. 5, the mobile station changes the reference pilot powerlevel to be used by the mobile station itself according to the flowchartof FIG. 4, and the base station receives the RRI channel, and changesthe power control threshold value to the R_(eff)(i) indicated by the RRIchannel.

If this method is used, the case that the power control threshold valueused in the base station is set to be lower than the reference pilotpower level used in the mobile station does not proceed. Also, thereference pilot power level for any data rate in variable data rateoperation is guaranteed to be the reference pilot power level definedfor the data rate which is lower than the present data rate by at most Nstage. In other words, the reference pilot power level for the presentdata rate is guaranteed to be at least the reference pilot power leveldefined for the data rate that is lower than the present data rate by Nstage. Generally, if N is 2, it is possible according to the presentinvention that the mobile station uses at least the reference pilotpower level for the data rate that is lower than the present data rateby at most 2 stage, and this enables the operation of the variable datarate without great loss of the performance. For example, if theeffective data rate currently transmitted is 76.8 kbps and N is 2, theminimum reference pilot power level for this data rate in variable rateoperation is guaranteed to be the reference pilot power levelcorresponding to 19.2 kbps that is lower than the present data rate by 2stages in transmission of 76.8 kbps.

Also, as described above, it can be prevented that the base station usesthe power control threshold value that is lower than the reference pilotpower level used by the mobile station, and thus propagation of theerroneous power control can be prevented.

In summary, if the mobile station has any packet to be sent by themobile station itself, it starts transmission of the packet always withthe lowest data rate of 9.6 kbps without permission of the base station.

Thereafter, the base station generates the dedicated RRC bit using thequality information of the reverse channel and so on, and the mobilestation starts the adjustment of the transmission data rate through theRRC bit.

In the above-described adjustment process, the mobile station and thebase station changes the pilot power level to be used according to apredetermined engagement and the threshold value to be used during thepower control process. At this time, as described above, one among themethod using the upper signaling message, the method using the indicatorchannel of a physical layer, and the method of changing the referencepilot power level and the power control threshold value by the mobilestation and the base station, respectively.

As described above, according to the present invention, a communicationsystem that provides a satisfactory performance with respect to allpossible reverse data rates supported in the variable data rate mode canbe constructed.

Especially, the present invention can construct a communication systemthat provides a satisfactory performance with respect to all possiblereverse data rates supported in the variable data rate mode by using amethod of changing the reference pilot power level to be used by themobile station and the power control threshold value to be used by thebase station according to the data rate in the variable data rate modefor reverse transmission of packet data.

It will be apparent to those skilled in the art than variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of adjusting a signal power in a variable data rate mode ina mobile communication system, comprising: allocating a reference pilotsignal level to each of a plurality of data rates supported by thesystem; adjusting the reference pilot signal level for a changed datarate based on an external control information; and adjusting a powercontrol threshold for secondly adjusting the reference pilot signallevel corresponding to the reference pilot signal level.
 2. The methodof claim 1, wherein the external control information is dedicated ratecontrol information for a reverse link.
 3. The method of claim 1,wherein the power control threshold is used for generating a powercontrol bit for commanding to control the reference pilot signal level.4. The method of claim 1, wherein the data rates supported by the systemare classified into a predetermined number of groups, and the power ofthe pilot signal is designated for each of the groups.
 5. The method ofclaim 5, wherein the power control threshold is adjusted in accordancewith the reference pilot signal level of a group to which the changeddata rate belongs.
 6. The method of claim 5, wherein one group includesat least two data rates duplicative of the other.
 7. The method of claim1, wherein the reference pilot signal level and the power controlthreshold are simultaneously adjusted.
 8. The method of claim 7, whereinone transmits information of the changed data rate to the other througha reverse link rate indicator channel in order to simultaneously adjustthe reference pilot signal level and the power control threshold.
 9. Themethod of claim 8, wherein the other adjusts the power control thresholdin accordance with the reference pilot signal level corresponding to thechanged data rate.
 10. The method of claim 7, wherein the reverse linkrate indicator channel further includes a time index of a frame throughwhich information of the changed data rate is transmitted in order tosimultaneously adjust the reference pilot signal level and the powercontrol threshold.
 11. The method of claim 1, wherein wherein thereference pilot signal level is increasingly adjusted after a prescribeddelay or decreasingly adjusts it without a delay in accordance with thechanged data rate.
 12. The method of claim 11, wherein information ofthe changed data rate is transmitted through a reverse link rateindicator channel.
 13. The method of claim 12, wherein the power controlthreshold is adjusted in accordance with the reference pilot signallevel corresponding to the changed data rate.
 14. A method of adjustinga signal power in a variable data rate mode in a mobile communicationsystem, comprising: classifying the data rates supported by thecommunication system into a predetermined number of groups; allocating areference pilot signal level to each of the data rates; reporting achange of the data rate group to a different group if a changed datarate based on an external control information is the highest or lowestdata rate among the data rates which a group includes; adjusting a powercontrol threshold for adjusting the reference pilot signal level aftertransmitting a change-approval message in response to the reporting; andadjusting the power of the pilot signal corresponding to the changedgroup. after receiving the approval message.
 15. The method of claim 14,wherein the external control information is dedicated rate controlinformation for a reverse link.
 16. The method of claim 14, wherein thepower control threshold is used for generating a power control bit forcommanding to control the reference pilot signal level.
 17. The methodof claim 14, wherein one group includes at least two data ratesduplicative of the other.
 18. The method of claim 14, furthercomprising: maintaining a prescribed reference pilot signal levelallocated for the group; changing a prescribed traffic signal leveldefined for each data rate; wherein the changed data rate is not thehighest or lowest data rate among the data rates which a group includes.19. A method of adjusting a signal power in a variable data rate mode ina mobile communication system, comprising: determining a data rate basedon an external control information; continuously transmittinginformation of the determined data rate for a predetermined time;adjusting a power control threshold for adjusting a reference pilotsignal level by monitoring the transmitted information for thepredetermined time; and adjusting the reference pilot signal level fortransferring data in accordance with the changed data rate after thepredetermined time.
 20. The method of claim 19, wherein one transmitsinformation of the changed data rate to the other through a reverse linkrate indicator channel.
 21. The method of claim 20, wherein the powercontrol threshold is adjusted in accordance with the reference pilotsignal level corresponding to the changed data rate.
 22. The method ofclaim 20, wherein the reverse link rate indicator channel furtherincludes a time index of a frame through which information of thechanged data rate is transmitted.
 23. The method of claim 19, whereinthe determined data rate is maintained for the prescribed time withreference pilot signal level maintained to the previous value andtraffic signal power level is changed to the level defined for thedetermined data rate.
 24. The method of claim 19, wherein the powercontrol threshold is maintained for the prescribed time, and the changof power control threshold is performed after the prescribed time whencorrectly decoding the present data rate indicated on the reverse rateindication channel at least once during the prescribed time period. 25.The method of claim 19, wherein the external control information isdedicated rate control information for a reverse link.
 26. The method ofclaim 19, wherein the power control threshold is used for generating apower control bit for commanding to control the reference pilot signallevel.
 27. A method of adjusting a signal power in a variable data ratemode in a mobile communication system, comprising: determining aneffective data rate changed from a present frame (i.e., i-th frame)based on an external control information; comparing the determined datarate with each data rates of previous N frames; and adjusting areference pilot signal level for transferring data according to a resultof comparison; and adjusting a power control threshold for secondlyadjusting the reference pilot signal in accordance with the referencepilot signal level corresponding to the changed data rate.
 28. Themethod of claim 27, wherein if the effective data rates for a delay timeof the N frames are larger than or equal to the effective data rate atan (i−N)-th frame time, the reference pilot signal level of the presentframe is set as the reference pilot signal level before the N frames.29. The method of claim 27, further comprising the steps of: comparingthe reference pilot signal level defined against the effective data rateat the present frame with the reference pilot signal level used in aprevious (i.e., i−1-th frame time) frame if at least one data rate amongthe previous N frames is smaller than the effective data rate at an(i−N)-th frame time; and adjusting the reference pilot signal level inaccordance with the result of the comparision.
 30. The method of claim29, wherein the determined data rate is a combined data rate of achannel for transmitting a new packet and a channel for transmitting apacket whose retransmission is requested.
 31. The method of claim 29,wherein one transmits information of the changed effective data rate tothe other through a reverse link rate indicator channel.
 32. The methodof claim 31, wherein the power control threshold is adjusted inaccordance with the reference pilot signal level corresponding to thechanged data rate.
 33. The method of claim 27, wherein the externalcontrol information is dedicated rate control information for a reverselink.
 34. The method of claim 27, wherein the power control threshold isused for generating a power control bit for commanding to control thereference pilot signal level of the mobile station.
 35. A method ofadjusting a signal power in a variable data rate mode in a mobilecommunication system, comprising: allocating a reference pilot signallevel for transferring data to each of a plurality of data ratessupported by the system; changing a transmission data rate according tothe data rate control information; and changing a level of a pilotsignal according to the changed transmission data rate.